How important are presentation skills for a pmm? How do I develop these skills?

I'd say presentation skills are pretty critical for a PMM. I've often heard other say that PMMs create "pretty slides" jokingly, but everyone knows we do far much more than that in developing positioning, messaging, enablement materials, etc. I'll I'd admit, I'm still working becoming a better presenter myself ;) 

Because we work in such a cross-functional manner, communication skills are pretty key and presentation skills are a tool in that arsenal. We are successful because we effectively share information that enables teams to go-to-market with products and this often take the form of presenting to others. One could say the most successful PMMs are also great at pitching and building trust with their counterparts which is a higer level skill in giving presentations. 

The good news is that presentation skills can be developed in many ways, from getting a Toastmasters certification to asking a presenter at your company that you admire to mentor. Start to study presentations and figure out why some are better than others. Since practice makes better, I'd also look for speaking opportunities outside of the company, at alumni events, industry meet ups, podcasts, etc. There are lots of opportunites out there.   

I honestly think it depends in the type of PMM you want to be.

If you want to be in rooms where decisions are made and influence those, I’d say yes it’s a very important skill. Even if you’re only focused on market research, there will be a time to present your findings so everyone can see how awesome you are and what great insights you have.

Presenting as a PMM doesn’t only happen for folks who wants to take center stage and demo a product at a conference, it happens every day when you have convos with Sales, when you present strategy to your Marketing team, and when you go through the findings from your win/loss analysis because your C-suite has to see it.